Earth-moving machines, such as track type tractors, hydraulic excavators, and the like, frequently operate in severe environments, which submerge drive line components, such as final drives and the like, in a slurry of mud, water, and other injurious debris. The final drives of such machines may have a split housing containing gears and bearings which must remain lubricated and free of contaminants in order to operate properly over an extended period of time. The split housing of such final drives has a first member which remains stationary and a second member which rotates about the axis of the drive axle relative to the first member. A metal-to-metal face-type seal is frequently is used in such applications to seal lubricating oil in and debris out of the final drive housing. Such metal-to-metal face seals serve as the primary oil seal and may be of any suitable type, such as disclosed in U.S. Pat. No. 3,180,648, which issued Apr. 27, 1975 to Kupfert et al., and U.S. Pat. No. 3,905,607, which issued Sep. 16, 1975 to Roy L. Maguire et al., both of said patents being assigned to the assignee hereof. The seals, while satisfactory for normal operation, are found to have some drawbacks when the environment becomes too severe, particularly when the final drive housing is submerged in a watery slurry of mud, sand and other abrasive materials. In such conditions, the slurry of mud can flood the passageway to the primary metal-to-metal seal. If the rotatable member of the split housing is not perfectly true, the housing can rotate in an eccentric pattern which may cause a pumping action which forces the slurry of mud under substantial pressure against the metal-to-metal seal. As a result, such contaminants can be forced past the primary seal and into the lubricated gear chamber of the final drive. Another problem of the prior art seals is that the pumping action of the slurry forces dirt and grit between the sealing faces of the metal-to-metal seal which produces excessive wear and early failure of the primary metal-to-metal seal.
Secondary seals have been used in the past in an attempt to protect the primary seal against such abrasive slurries. However, such prior secondary seals have met with only limited success because of their construction. Such secondary seals typically have been constructed from lengths of rope or other material, which have a pair of ends that must be joined together, either mechanically with staples or the like, or chemically with an adhesive. Either type of joint connection is generally less strong in tension than the seal material itself, thus causing a weak link. This weak link frequently fails, allowing the ends to separate.
Also, prior secondary seals do not have a particularly hard sealing face, which causes a high wear rate in the presence of the abrasive and non-lubricated environment in which such secondary seals are intended to operate.
The present invention is directed overcoming one or more of the problems set forth above.